This gear is only needed if you are refilling STARTER* cartridges for the Brother TN210, since the starter cartridges don't always have this reset gear installed. The printer displays a "toner life end" message if no reset gear is detected. A reset gear must be installed on any used TN210 starter cartridge (any color) in order for the printer to function properly once the cartridge has been refilled and re-installed in the printer.

* A starter cartridge is the cartridge that ships free with your printer. If you purchase the cartridge separatley, you will not require this gear.